The present invention relates to the field of floating gate semiconductor devices. More particularly, but without limitation thereto, the present invention is directed to limiting the voltage across a tunnel or injection oxide in a floating gate device.
An electrically programmable floating gate device, such as a non-volatile EEPROM cell or a non-volatile analog memory element, may comprise a floating gate insulated from a programming terminal by a dielectric across which electrical charge is injected or transferred. The rate of charge transfer across the dielectric to the floating gate during the application of a programming voltage depends on the charge resident on the floating gate. The resident charge influences the electric potential of the floating gate, and thus the voltage difference across the charge injection dielectric, in such a way as to oppose further injection of charge having the same polarity. The dependence of the injection current on the voltage across the charge injection dielectric is generally non-linear. Limiting or regulating the voltage across the charge injection dielectric is desirable in floating gate devices, such as non-volatile analog memory elements used in adaptive circuits, to insure that increments/decrements of charge on the floating gate are relatively constant over at least part of the range of total charge on the floating gate.
A need thus exists for a floating gate device that may be programmed with increments/decrements of charge without opposition from the resident charge on the floating gate. The present invention is directed to these needs and may provide further related advantages.